Family doctor's first to be sympathetic (4)
I believe the answer is:
kind
'be sympathetic' is the definition.
('kind' can be similar in meaning to 'sympathetic')
'family doctor's first' is the wordplay.
'family' becomes 'kin' ('kin' can be a synonym of 'family'**).
'first' indicates taking the first letters.
The initial letter of 'doctors' is 'd'.
'kin'+'d'='KIND'
'to' acts as a link.
(Other definitions for kind that I've seen before include "Tender-hearted" , "Benevolent - variety" , "Friendly, generous and considerate" , "Sort; gentle" , "Generous - type" .)